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MEH * > S8 Hypothalamic Pituitary Axis and Growth Hormone > Flashcards

S8 Hypothalamic Pituitary Axis and Growth Hormone Flashcards

1
Q

What processes do the hypothalamus and pituitary gland modulate?

A
  • body growth
  • milk secretion
  • reproduction
  • lactation
  • adrenal gland function
  • thyroid gland function
  • water homeostasis
  • puberty
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2
Q

What are the two parts of the pituitary gland?

A

Anterior and posterior gland

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3
Q

What is the embryological origin of the anterior pituitary gland?

A

Arises the evagination of the oral ectoderm (Rathke’s pouch) which is primitive gut tissue

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4
Q

What is the embryological origin of the posterior pituitary gland?

A

Originates from the neuroectoderm which is primitive brain tissue

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5
Q

What connects the hypothalamus to the pituitary gland?

A

The infundibulum (pituitary stalk)

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6
Q

What is released from the posterior pituitary?

A
  • oxytocin

* antidiuretic hormone (ADH)

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7
Q

Where are oxytocin and ADH produced?

A

Produced by neurosecretory cells in the supraoptic and paraventricular nuclei of the hypothalamus

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8
Q

What type of signalling transports oxytocin and ADH to the posterior pituitary?

A

Neurocrine signalling

Transported down nerve cell axons

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9
Q

Where are hormones that act on the anterior pituitary synthesised in the hypothalamus stored before release in the hypophyseal portal system?

A

Stored in median eminence

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10
Q

What is the hypophyseal portal system?

A

Between the hypothalamus and pituitary gland - connection of two capillary beds

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11
Q

What action do hormones that are released from the hypothalamus to act on the anterior pituitary have?

A

Stimulate or inhibit target endocrine cells in anterior pituitary (via neurocrine signalling)

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12
Q

What do endocrine cells in the anterior pituitary do?

A

Secrete a variety of hormones into the blood stream to act on distant target cells (endocrine signalling)

Also have autocrine and paracrine functions

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13
Q

What does oxytocin do?

A

Involved in the milk let down reflex and uterus contractions during birth

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14
Q

What does ADH do?

A

Regulation of body water volume

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15
Q

What are the 6 tropic hormones of the hypothalamus?

A
  • thyrotopin releasing hormone (TRH)
  • prolactin release-inhibiting hormone (PIH) (dopamine)
  • corticotropin releasing hormone (CRH)
  • gonadotropin releasing hormone (GnRH)
  • growth hormone releasing hormone (GHRH)
  • growth hormone-inhibiting hormone (GHIH) (somatostatin)
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16
Q

What does tropic mean?

A

Affect the release of other hormones in the target tissue

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17
Q

What 6 hormones are produced by the anterior pituitary?

A
  • thyroid stimulating hormone (TSH)
  • adrenocorticotropic hormone (ACTH)
  • luteinising hormone (LH)
  • follicle stimulating hormone (FSH)
  • prolactin (PRL)
  • growth hormone (GH)
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18
Q

On which gland does TSH act? What does it cause the release of?

A

Thyroid gland

Thyroid hormone (T3 and T4) which affect metabolic rate

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19
Q

On which gland does ACTH act? What does it cause the release of?

A

Adrenal gland

Cortisol part of the stress response and involved in metabolic actions

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20
Q

On which gland does prolactin act? What it cause the effect of prolactin?

A

Mammary glands

Breast growth and milk secretion

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21
Q

On which tissues does growth hormone act? What does it cause the release of?

A

Liver and many tissues

IGFs released from liver for growth

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22
Q

On which gland does LH act? What does it cause the release of?

A

Ovaries in females, testes in males

Sex hormone secretion

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23
Q

On which gland does FSH act? What effect does it have?

A

Ovaries in females, testes in males

Gamete production

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24
Q

How are the pathways of hypothalamic and anterior pituitary hormone release/production regulated?

A

By negative feedback

25
Q

What is the hypothalamic-pituitary-adrenal axis?

A

Stress occurs (pain, fever, etc) casing the hypothalamus to release CRH which stimulates the anterior pituitary to release ACTH which stimulates the adrenal cortex to release cortisol which acts on target tissues

Cortisol inhibits the anterior pituitary releasing ACTH and the hypothalamus releasing CRH

26
Q

What factors influence growth?

A
  • genetics
  • nutrition
  • environment
  • hormones e.g. growth hormone
27
Q

Where is growth hormone produced? What is it stimulated by, what is it inhibited by?

A

Produced in anterior pituitary

Stimulates by hypothalamic GHRH, inhibited by hypothalamic somatostatin

28
Q

What type of hormone is growth hormone? How is it folded properly?

A

A protein hormone that has a signal peptide that needs to be cleaved before proper folding can occur

29
Q

How are the growth-promoting effects of growth hormone usually exerted?

A

Exerted via insulin-like growth factors (somatomedins) - GH causes the liver and skeletal muscle to produce and secrete IGFs

30
Q

Why is GH essential for normal growth during childhood and teenage years?

A
  • it stimulates long bone growth (length and width before epiphyseal closure, width after)
  • IGFs stimulate bone and cartilage growth
31
Q

Why are GH and IGFs essential in adults?

A
  • help maintain muscle and bone mass
  • promote healing and tissue repair
  • modulate metabolism and body composition
32
Q

When is GH secretion at it’s highest?

A

During deep sleep

33
Q

Does REM sleep decrease or increase GH secretion?

A

Decrease

34
Q

Does stress increase or decrease GH secretion?

A

Increase

35
Q

Does exercise increase or decrease GH secretion?

A

Increase

36
Q

What does a decrease in glucose and/or fatty acids mean for GH secretion? So what does an increase in glucose or free fatty acid lead to?

A

GH secretion increases

A decrease

37
Q

In fasting and obesity does GH secretion increase or decrease?

A

Fasting - increase
Obesity - decrease

Increases in fasting to break down fatty tissue to release energy

38
Q

What is GH secretion related by in terms of negative feedback?

A
  • long loop - mediated by IGFs - they inhibit release of GHRH from hypothalamus, stimulate release of somatostatin from hypothalamus and inhibit the release of GH from the anterior pituitary
  • short loop - mediated by GH - stimulates somatostatin release
39
Q

What is the name of a growth hormone deficiency in childhood?

A

Pituitary dwarfism

40
Q

What is pituitary dwarfism? What are the signs of it? How is it treated?

A
  • proportionate type of dwarfism
  • can be a complete or partial deficiency
  • growth rate is slower than normal
  • there’s delayed or no sexual development during teenage years
  • height is below 3rd percentile on standard growth charts
  • treated with GH therapy
41
Q

What is the name of the growth hormone excess condition that occurs in childhood?

A

Gigantism

This is rare

42
Q

What is the name of the growth hormone excess condition that occurs in adulthood?

A

Acromegaly

Large extremities e.g. hands, feet, lower jaw

43
Q

How does GH exert its effects on cells?

A

GH receptors activate Janus kinases (JAKs) - tyrosine kinase receptors and these receptors cause activation of signalling pathways that lead to transcription factor activation and IGF production

44
Q

What are the 2 IGFs in mammals? What is each mainly involved in?

A

IGF1 - major growth factor in adults

IGF2 - mainly involved in fetal growth

45
Q

What modulates the availability of IGFs?

A

Binding proteins

46
Q

What type of signalling actions do IGFs carry out?

A

Paracrine, autocrine and endocrine

47
Q

What do IGFs act through? What are their actions?

A

IGF receptors

Hypertrophy (cell growth), hyperplasia (cell number increase), increase in rate of protein synthesis and increase in rate of lipolysis in adipose tissue

48
Q

Insulin and IGF1 can act on the same receptor, what is this receptor? What is the main effect of this receptor type?

A

A hybrid receptor

The main effect from this receptor are mitogenic effects

49
Q

The effects of insulin and IGF1 are both metabolic effects and mitogenic effects, which has the main effect on metabolism and which on mitosis?

A

Metabolism - insulin

Mitosis - IGF1

50
Q

What is the growth related action of insulin?

A

Enhances somatic growth and interacts with IGF receptors

51
Q

What is the growth related action of thyroid hormones?

A

Promote CNS development and enhance GH secretion

52
Q

What is the growth related action of androgens?

A
  • accelerate pubertal growth spurts
  • increase muscle mass
  • promote closure of epiphyseal plates
53
Q

What is the growth related action of estogens?

A
  • decrease somatic growth

* promote closure of epiphyseal plates

54
Q

What is the growth related action of glucocorticoids?

A

Inhibits somatic growth

55
Q

What can IGF1 do in some tissues? How does this relate to tumours?

A

Inhibits apoptosis

Some types of tumours express abundant ICF1 receptors to inhibit apoptosis

56
Q

When can synthetic oxytocin, pitocin, be administered? And why?

A

To increase uterine tone and control bleeding after birth and to help induce uterine contractions during birth

Oxytocin/pitocin bind too oxytocin receptors on uterine smooth muscle cells and activate uterine contractions

57
Q

What is another role of ADH/vasopressin other than reabsorption of water in the kidneys? What is a clinical advantage of this?

A

Increase peripheral vascular resistance by activating ADH receptors on smooth muscle cells of blood vessels and causing vasoconstriction which increases arterial blood pressure

Restoring blood pressure in hypovolaemic shock during haemorrhage

58
Q

What hormone does TRH have a minor positive control on?

A

Prolactin

59
Q

Why is prolactin releasing hormone (PRH) not often considered one of the tropic hormones of the hypothalamus?

A

Because it may not exist

MEH * (22 decks)

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